Among others, the heat dissipation and power saving are two important design issues for many computers, especially for notebook computers.
It is known that when the internal temperature of a computer is too high, the computer may malfunction or hang up. Generally, a cooling apparatus including a fan, a heat sink, or a heat pipe, is used to dissipate heat to lower the internal temperature. The cooling apparatus is typically designed in accordance with a predetermined TDP (thermal design profile) value.
However, instead of being a constant value, the actual power consumed by the CPU varies with the application problem executed. For example, a typical application, such as WORD, consumes power of 25 W. Thus, the cooling apparatus could be designed as having a lower TDP value. But, a 3D computer game application consumes power for at least 65 W. Thus, the cooling apparatus must have a higher TDP value for this application. However, it is in general difficult to design a cooling apparatus with a very high TDP value. The higher the TDP is, the higher the cost of cooling apparatus is.
Since a conventional design for cooling apparatus is not sufficient for the higher power heat dissipation issue, one method used nowadays detects the temperature value of the CPU. When the temperature value is beyond a limit, the clock speed of the CPU will be throttled to lower the heat generated. However, throttling the clock speed of the CPU will inevitably slow down the operation of the electronic system.
In fact, the temperature value is not a precise parameter for determining the running clock speed, since the temperature value is a result of accumulation of the heat generated by the CPU. It is too late to throttle the clock speed as the temperature value has been out of the limit indicating undesired amount of heat has accumulated already inside the CPU. The CPU will hang up if the accumulated heat can not be dissipated right away. Therefore, many designers generally adjust the clock speed down to fifty percent to avoid the damage. However, the actual performance of the CPU will drop substantially when working at a lower clock speed.
It is apparent that heat inside the CPU keeps accumulating during the period in which the clock speed is being throttled. Therefore, the CPU might hang up right before throttling operation is complete. In order to take the time factor into consideration, the designers have to either expand the default tolerable limit or raise the TDP value.
It is also known that increasing the rotational speed of cooling fan enhances dissipation of heat, but the elevated noise is undesired.
FIG. 1 is a schematic diagram illustrating variation of power and temperature of CPU according to an embodiment of the prior art. When a user executes a higher power-consumption application, from time T1 to T2, the power starts to increase. The temperature value does not vary immediately at this moment. From time T2 to T3, the power increases, and the temperature value gets higher and higher. However, since the temperature does not reach a limit, the prior art method does nothing right now. From time T3 to T4, some applications are terminated, the power starts to decrease, but the temperature value still gets higher and higher and finally reaches the limit. For this point, the electronic system starts to throttle the clock speed of the CPU. From time T4 to T5, the cooling apparatus can not sufficiently dissipate the heat inside the CPU, the electronic system keeps on throttling the clock speed of the CPU, even though the power decreases and the power-consumption applications has been terminated. As recited above, the prior art makes the electronic system continuously throttle the clock speed of the CPU as long as the heat accumulates inside the CPU. Therefore, the performance of the CPU decreases. It is apparent that the electronic system will work slowly even though the user has terminated the power-consumption applications when the accumulating heat is not dissipated sufficiently. For example, a CPU with 2 GHz clock speed only works at 1 GHz clock speed when the heat has not been dissipated sufficiently, even though the user only executes low power-consumption applications.
Furthermore, after time T7 in FIG. 1, the CPU is in an idle state and the temperature value decreases down below the limit. According to the prior art, the electronic system stops throttling the clock speed of the CPU. That is, the electronic system works at un-throttled clock speed in the idle state. As to the power-saving issue, it is noted that the prior art wastes power in the idle state. This kind of power waste is a serious issue for many computer systems, especially for notebook computers
Therefore, a novel apparatus or method is desired to overcome the problems mentioned above.